Cold cutting technique for half-tone electronic engraving



Jan. 22, 1963 s. w. LEVINE COLD CUTTING TECHNIQUE FOR HALF-TONE ELECTRONIC ENGRAVING Filed Dec. 25, 1959 DRIVER MIXER & Powk AMP.

scIZEEN BALANCE AMPLIFIER HILL & DALE BALANCE A MPLlF/ER CLIPPER 6- WAVE SHAPER 1 PH. INVEQT. .J

AMPLIFIER AND 534 MUEI. W. 1. E v//v, INVENT OR.

A rr X JouBLE- FEEQ P ts United States Patent 3,075,042 COLD CUTTING TECHNIQUE FOR HALF-TONE ELECTRONIC ENGRAVING Samuel W. Levine, Westbury, N.Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Filed Dec. 23, 1959, Ser. No. 861,625 7 Claims. (Cl. 178-66) This invention is concerned with improvements in electronic half-tone engraving, and has for its principal object the provision of an apparatus and method, by which half-tone engraved plates of good printing and matting quality can be produced by the cold engraving of plate material in a manner generally analogous to the production of similar plates by the hot burning of plastic plate material. The invention thus provides for the provision of metal engravings, for example on magnesium or magnesium-alloy plate stock, by the electronic line scan and point-to-point engraving procedure currently in wide use by newspapers and other printing plants.

The known apparatus and techniques referred to above are best exemplified by the disclosure of U.S. Reissued Letters Patent 23,914 of December 21, 1954, to J. A. Boyajean, Jr., owned by the assignee of the present invention, utilizing the heated plate-deforming tool therein described as the preferred plate-deforming tool, and operating upon a thin plate composed for example of a heat-decomposable material such as cellulose nitrate. Preferred forms of the latter material are disclosed in US. Patent No. 2,827,726, G. F. Stradar, also owned by the present assignee.

At the present time, there are three principal types of machines for the cold engraving of half-tone printing plates direct from electrical signals. In the first type (exemplified by the Klischograph machine of Dr. Rudolph Hell), a fiat-bed machine uses a linear scan motion to produce a screened reproduction quite similar in structure to the desired conventional pattern, but it is necessary to rotate the copy and the plate at a 45 degree angle to the direction of scan, which can only be done by scanning a diagonal of the copy, rather than lines parallel to the rectangular copy edges. The size of copy (and plate) which a given machine can handle is therefore considerably reduced. In a second type (exemplified by the Elgrama machine of Swiss origin), a hilland-dale type of engraving is utilized resulting in a line pattern; while theoretically this machine can scan and engrave in the directions parallel to copy edges, operators find it necessary, as a practical matter, to restort to 45 degree rotation of the copy and plate to minimize the line characteristic of the screen, and to reduce the problem of ink flow which reduces detail in the shadow areas of the plate. In a third type of machine (which has been demonstrated experimentally by Hassing), a triangular shaped dot is engraved, to circumvent the requirement for rotating the copy. The screen so produced is not conventional, in that the dots are aligned at a 60 degree angle instead of the usual 45 degrees characteristic of the standard screen; the dot shape also raises other problems.

In the engraving technique to be described herein, a somewhat unconventional dot structure is obtained, but one whose differences from the standard are visible only on microscopic examination. When a printed proof from the plate is examined visually, it appears to be entirely conventional. The copy and plate can be oriented (as on a rotary type machine) with the direction of scan parallel to an edge of the copy, yet the rows of dots line up at the desired 45 degree angle. The achievement of this angular alignment is very important, because it happens that the human eye can resolve details much better when the detail is aligned in either a horizontal or vertical direcice tion, and resolves least when the details are aligned at the 45 degree angle. If a plate is engraved with the dots aligned vertically or horizontally, they become very apparent to the eye, which is objectionable since the entire basis for half-tone reproduction is the suppression of the effects of the individual dots in favor of the over-all impression of continuity of tones.

It is accordingly a further object of the invention to provide ways and means for accomplishing the electronic half-tone cold engraving of metal or like hard plate material, to yield in a single complete scanning operation a plate having the desired tonal range, proper dot structure and shape, and the other properties deemed requisite by those using such plates for printing operations.

It is a further object of the invention to provide ways and means for producing a cold engraved half-tone plate having the desired staggering of the dots of successive rows, without the necessity for cocking or the turning of the original copy and plate material at a 45 degree angle relative to the directions of scan; thereby making it possible to engrave plates of full size up to the normal limits of the engraving equipment employed.

Still another object of the invention is to provide an engraving system of the above type which can be carried out with rotary plate-handling machines such as described in the Reissue patent referred to above, with the copy and the plate oriented in the usual way, yet producing the desired diagonal or stagger pattern of dots in the finished plate. An additional object of the invention is to provide a system of this kind in which the deflection of the engraving tool employed is relatively smaller than in the case of normal hot-stylus engraving as employed heretofore with hot-stylus machinery, thereby to permit either a higher effective speed of engraving, or the production of steeper walls on the cavities in the plate material which form the dot structure. The depth of engraving for a given highlight dot size is also considerably less than that required for the cold engraving techniques as practiced in the three electronic engraving machines previously discussed.

Yet a further object of the invention is to provide such a procedure which is capable of producing a highlight dot of very minimum size as compared with prior art efforts in electronic plate engraving. Finally, it is an object of the invention to produce such a process and system which can be carried out with very simple and readily performed modifications in existing line-scan engraving equipment of the rotary cylinder type, thereby to permit a variety of different materials to be satisfactorily employed with such equipment.

Briefly to summarize the way in which the above and other objects of the invention are accomplished, it may be said that the invention utilizes a cold engraving tool shaped to engrave a cavity, in metal or like plate material, which is of diamond shapethat is, a square cavity oriented with its sides at 45 degrees to the principal scan directions. This is accomplished by a screen tone modulation of the engraving depth as carried out in the machine of the reissued patent mentioned heretofore. However, after the engraving of each complete line of such cavities in one direction of scan, the same tool is employed to produce either a variable-width engraved pattern or a double-frequency engraved pattern, which thus modifies the area lying between the successive rows of dots; but the production of the variable-width modification or the double frequency engraving is automatically restricted to plate regions in which highlight tones greater than some predetermined value are to be produced. The result is a plate pattern which in all tonal respects is fully equivalent to the more conventional pattern of staggered square dots of varying size.

With the above outline of the invention in mind, the

It; actual procedures employed, and preferred apparatus for carrying out such procedures, will best be understood from the following detailed specification of a preferred example thereof, taken in connection with the accompanying drawings, in which:

FIGURE 1 is an illustration of the cavity structure (or dot structure) of a conventional electronicallyengraved plate, showing a variety of tonal values in the dot pattern.

FIGURE 2 is a similar illustration of the dot structure obtained by the use of the present invention with the hilland-dale variable width auxiliary engraving, together with an indication of the manner in which it is obtained.

FIGURE 3 is a similar illustration of the dot structure obtained by the use of the present invention utilizing the double frequency auxiliary engraving line, together with an indication of the manner in which it is obtained.

10. Such plates are printed'by inking the printing surface,

so the surface at the left end of FIGURE 1 corresponds to a shadow tone in the reproduction. The dot structure consists of alternately staggered rows of square indentations cavities 12 whose area, at the printing surface, is a relatively small fraction of the total undisturbed area surrounding each dot, In the central portion of FIGURE 1, a middle-tone dot structure 14 is indicated, in which the cavity area has increased to a larger fraction, specifically to a fraction greater than one-half; This is possible because the square-topped cavities produced bythe pyramidal engraving stylus point actually overlap at the printing surface, as indicated by the dash lines at the corners.

Between the areas 12 and 14, a single row of dots is shown.

light dot pattern. In all cases, the dots are substantiallyrectangular in outline, and arranged so that the nearest dots extend at a 45 degree angle to the vertical and horizontal edges of the original rectangular copy and engraving material. In effect, the arrangement of nearest dots lining up at a 45 degree angle to the horizontal and vertical makes them less easily resolved by the eye, and this is a condition that is desired.

It will be seen from the foregoing that production of such a staggered dot pattern cannot be accomplished by the engraving of continuous lines along directions parallel to the plate edges, but that such could be attempted by erforming variable-width line engraving along two sets of mutually perpendicular lines cocked at 45 degrees to the plate edges; or alternatively by cocking the original copy (and the plate material) at such angle. In FIGURE 1, the scanning and engraving line direction is from top to bottom of the figure.

According to the invention, an acceptable cold-engraved dot pattern equivalent to the known FIGURE 1 pattern can be obtained, on a single pass of the plate material, which can be arranged at the normal angle with its edges parallel to the scan directions, by the use of a pyramidal cold engraving tool which is'however angled at 45 degrees so as to engrave diamond-shaped dots such as indicated in the shadow portion 18 at the left of FIGURE 2. As the penetration depth increases, the excised diamond-shaped areas become larger, as; at 20, but in this,v case the ,signal'is appropriately limited to prevent the corners of these cavities from overlapping or touching. The middle tone area is thus represented by a grid of perpendicular printing-surface lines 22, the minimum width of such lines being set by the controls of the process.

Further, according to one form of the invention, the highlight area at the right end of FIGURE 2 is obtained by removing controlledwidth furrows of the connector grid lines 22 between each pair of their intersection centers from top to bottom of the plate material, being the scan direction of the process. These furrows 24 (shown stippied for clarity) are produced by the same stylus which excised the cavities in the other plate portions, the stylus having a relatively shallow included angle at its pyramidal point so that the width of the furrow is readily controlled by the penetration depth, in the manner of a hill-and-dale recording of the Philips-Miller type. The result, as indicated in FIGURE 2, is a highlight dot area 26 consisting essentially of controlled portions of the intersections only of the watlie-pattern middle tone area 20'. It will be noted that the production of a continuously varying furrow is readily accomplished by eliminating the on-off tone which characterizesthe driving current of the stylus in the true dot-producing action in the shadow and middle tone. regions.

In order to permit a plate as illustrated in FIGURE 2 to be produced in a single scan of the material, the vari able width lines or furrows 24 are preferably produced (when required by the tones value being engraved) by the use of the engraving stylus as a continuous hill-and-dale graver upon alternate passes of the stylus along the scan lines running from top to bottom of the drawing figures. In this connection, it will be recalled that the staggering of the dot patterns of the conventional engraving in FIGURE 1 is obtained by the use of a 180 degree phase shift in the screen tone (or on-off tone) during alternate lines of scan or engraving. The same procedure is used for the dot structure of FIGURE 2, but the on-off tone is completely suppressed during the production of the variable width furrows 24. Thus, the scan cycle is made up of a sequence of four conditions, rather than two, in regions of highlight tone production: I

(l) A line of dots with the screen tone on, phased zero degrees.

(2) A line engraving with the screen tone on.

(3) A line of dots with the screen tone on, but phased 180 degrees.

(4) A line engraving with the screen tone off.

Since the furrow width, from point to point along its direction, will have to be controlled independently from the penetration of the stylus when making a purely dot pattern, alternate control channels are provided to produce the desired output signals for the control of stylus during successive lines of engraving, as will be described.

In FIGURE 3, an alternate to the technique of FIG- URE 2 is pictured. In this case, the hill-and-dale auxiliary line is replaced by a line of dots formed with the stylus operating at double the frequency of the primary engraving frequency. This technique has the advantage over the hill-and-dale system in that it can engrave to a greater depth where the connectors are being removed, and thereby reduce the elevation of the remaining connector to a greater degree. This is desirable in that, if

too great a pressure is used in the printing process, ink is not deposited on the shallow connectors and thereby printed. The scan cycle for producing the plate as depicted in FIGURE 3 would occur in the following sequence:

(1) A line of dots with the single frequency tone on, phased zero degrees.

(2) A line of double frequency dots with a phase shift of 90 degrees.

(3) Aline of single frequency dots with the screen tone on, but phased 180 degrees with respect to the first line of single frequency dots.

(4) A line of double frequency dots with phasing at 90 degrees to the previous line of single frequency dots.

It has been found that plates engraved with this double frequency technique, when sterotyped by the newspaper process referred to as matting, produce much better reproductions that the dot structure formed by the hill-anddale technique first described.

Experience with the coldengraved patterns made according to the invention demonstrates that while the highlight dot is not perfectly square, it does correspond closely to a rectangular shape, occasionally somewhat elongated in the direction of scan, and with a slight dimple in each edge as indicated at 28 in FIGURE 2. However, it has been found possible to produce an effective dot size (at the printing surface) as small as 0.001 inch on the side. Moreover, the presence of the connectors or grid lines 22 in the middle tone region has been found distinctly advantageous, since their presence eliminates the so-called half-tone break between shadow and middle tone regions. Furthermore, the fact that the stylus penetration is never so great as to permit an overlap of the excised cavities, permits faster operation of the stylus in its reciprocating motion, and in turn permits either a faster engraving action or the production of steeper-walled cavities, both of which are desirable features.

It will be apparent to those skilled in this art that the provision of a single machine for carrying out the foregoing procedures will also make it readily possible to produce line engravings as such, by simple changes in the line advance rate and complete suppression of the on-oif or screen tone. Thus, a machine can be produced which will be capable of conventional hot-burning, cold halftone engraving, or direct line work.

FIGURE 4 of the drawings shows schematically one form of apparatus by which the novel methods may readily be practiced. The mechanical parts of the equipment are quite similar to the machine of the Boyajean Reissue patent, including a drive motor 30 and gearing by which are rotated the cylinder 32 for carrying an original continuous tone image such as a news photo or the like and the cylinder 34 for carrying the plate to be engraved with a half-tone reproduction of the image. A scanner carriage 36 carries the usual focussed spot light source 38 and the photocell pickup 40, while an engraver carriage 42 supports the usual stylus drive motor 44 operative to drive the stylus 46 toward and away from the plate surface for dot production. The two carriages are connected for concurrent axial motion (parallel to the axes of the cylinders) by a drive connection 48 from the same motor power source. Suitable guides, bearings and the like have been omitted from the drawing in the interest of simplification of the illustration. A fixed-frequency tone-wheel 50, as described in the reissue patent, or of other known type, provides the screen signal synchronized with cylinder rotation.

In the case of double frequency engraving, the double frequency signal is readily obtained by clipping the single frequency screen signal, differentiating it, amplifying, clipping, and then wave shaping. The 90 degree phase shift is obtained by well-known techniques.

Various switching arrangements may be employed to produce the desired dot-position stagger as between successive rows of engraved dots, the arrangement illustrated including a dot or tone frequency amplifier and phase inverter 52 providing outputs which are 180 degrees apart in phase position with respect to cylinder rotation, and a relay 54 is energized and de-energized, during successive groups of two complete rotations of the cylinders, to apply the screen tone in desired stagger phase to the amplifier, clipper and wave shaper 56. A relay 58 controls contacts 59 to permit the tone output to be interrupted entirely, during the second revolution of each such group of two revolutions, to prevent the screen tone from modulating the image signal during those revolutions in which, :because of the existence of a highlight region under 6 scanner cell 40, a simple hill-and-dale or varying width cut is to be made.

The signals derived from scanner cell 40 are amplified by a preamplifier 60, and, during alternate single revolutions of the cylinders, are applied to alternate compensating amplifier networks 62 and 64 for independent regulation of the functional relation between the input signal and the desired depth of penetration of the stylus 46 into the material of the engraved plate on cylinder 34. This switching is accomplished by contacts 66 operated by a relay 68, and the outputs of the two compensating channels are likewise synchronously switched as by another contact set 70 of the same relay 68. The respective signals are then conveyed to the balance amplifier 72 which provides a separate and independent level control for the dot and hill-and-dale operations, as by respective potentiometers 74 and 76.

In view of the fact that the screen tone is interrupted during the hill-and-dale or variable width cut, the alternate switching of the output of balance amplifier 72 can readily be accomplished by a second set of contacts 78 of relay 58.

From the description above regarding the four different conditions which will exist during the engraving of a highlight reproduction, it will have been realized that the change in phase of the screen tone applied as a modulation to the amplified output signal in final mixed amplifier 80 must take place only at the completion of two complete rotations of the cylinders, while the shift as between dot engraving and furrow engraving, when it happens, must occur after each single revolution. This can easily be provided in a number of obvious ways, including the use of two-to-one counter, or by use of stick or latch-type relays suitably triggered and released once every one or two revolutions. FIGURE 4 illustrates an arrangement in which the shaft of the cylinders drives the smaller gear of a two-to-one gear set 82, there being a half-circular cam 84 on the larger gear, arranged to close contacts 86 during each alternate rotation of the cylinders, and open them' during the intervening rotations. Additionally, the large gear of set 82 drives the small gear of a second twoto-o'ne gear set 88, whose larger gear also carires a halfcircular cam 90 engaging switch contacts 92 to close them during two rotations of the cylinders, and to open them during the next two revolutions. Closure of contacts 86 energizes relay 68 as already described to accomplish the desired transfer as between dot engraving and hill-anddale during alternate successive revolutions of the cylinders, at contacts 66 and 70, and also, over a branch conductor 94, energizes relay 58 to switch the output of ampliher 72 and to cut the tone modulation on or off at contacts 78 and 59.

During the next group of two cylinder revolutions, exactly the same sequence occurs, but in this case the phase position of the screen tone will be reversed degrees by the energization of relay 54 over conductor 96 from contacts 92. Thus, during the production of two successive engraved lines of dots, the desired stagger of position will result, while the intervening lines of furrowproduction, when called for by the highlight signals from scanner cell 40 (as modified by the characteristics of the compensating amplifiers 62 and 64 and the balance amplifier 72), will be obtained in the desired manner. The amplifier characteristics are so chosen,,as will be understood, that in no case will the engraved dot-forming cavities actually overlap, or even quite touch one another at their corners; this condition can be insured by the use of suitable and well-known signal shaping techniques, as indicated for the amplifiers 62 and 64.

From the method standpoint, it is clear that an equivalent engraved plate could be obtained by the use of two complete scans, all of the dot pattern and wafile-iron grid of FIGURE 2 or FIGURE 3 being engraved during one scan, and all of the furrow production or double-frequency engraving being obtained as a second operation.

However, there are manifest technical advantages in the single-operation procedure outlined, for example in re duction of the need for careful positioning of the stylus at the beginning of the second complete scan operation. Theoretically, at least, the furrowing or double frequency operation could even be performed as a first operation, followed by the half-tone dot production, and it is at least conceivable that a skillful operator could produce a printable plate ,by hand engraving according to the patterns suggested herein.

A further advantage in the line-by-line interchange of the dotand furrow (or dot and double-frequency dot), functions across the plate width isthat it enables the operator to obtain a complete appraisal of the progress of the work after each line orpair of lines, for example by the use of the stroboscopic microscope described in the Boyajean patent. I

While the invention has been disclosed herein in concomprising scanning a continuous tone. original line-byline to develop signals representative of its tone values;

engraving a suitable material line by line 'in' a discrete pattern of ,dot-producing diamond-shaped cavities sized in accordance with said signals to represent dark tones and middle tones and highlights of the original, with the cavity centers in successful lines diagonally staggered;

maintaining the maximum cavity size at a value insufiicient to produce overlapping of the cavities, and super imposing ascan line'fur row between successful rows of cavities in regions corresponding to highlights of the original, while controlling the instantaneous width of said furrow at a value corresponding to the particular highlight tone then being scanned, but not greater than that which is s'ufiicient to remove the grid line connectors extending between adjacent cavities in the engraved plate.

2. The method of engravinga complete range of tonevalues in a material to form a'stereotype for duplication, comprising'scanninga continuous tone original line-byline to develop signals representative of its tone values,-

engraving a suitable material line by line in a discrete patternof dot-producing diamond-shapped cavities in accordance with said signals to represent dark tones and middle tones and highlights of the original; with the cavity centers in successive lines diagonally staggered; maintain ing the maximum cavity size ata value insufli'cient to pro-.

duce overlapping of the cavities, and superimposing a double frequency engraved line between successive rows of cavities in regions corresponding to highlights of the':

original, while controlling the instantaneous depth of engraving of the double frequency line at a value correspond ing to the particular highlight tone then being scanned, but

not greater'than thatwhichis sufiicient to remove thegrid line connectors extending between adjacent cavities in the engraved plate.

3. Themethod of engraving a complete range of tone values in a material. to form a stereotype for duplication, comprising scanning a continuous tone original-'line-byline; todevelop signals representative of its tone values,

8 engraving a suitable material line by line in a discrete pattern of dot-producing diamond-shaped cavities sized in accordance with said signals to represent dark tones and middle tones and highlights of the original, with the cavity centers in successive lines diagonally staggered; maintaining the maximum cavity size at a value insuflicient to produce overlapping of the cavities, and superimposing an auxiliary engraved pattern between successive rows of cavities in regions corresponding to highlights of the original, while controlling the instantaneous depth of engraving of the auxiliary pattern at a value. corresponding to the particular highlight tone then being scanned, but not greater than that which is sufiicient to remove the grid line connectors extending between adjacent cavities in the engraved plate.

4. The method of engraving a complete range of tone values in a material to form a stereotype for duplication, comprising scanning a continuous tone original line-byline to develop'signals representative of its tone values, engraving a suitable material line by line in a discrete pattern of dot-producing diamond-shaped cavities sized in accordance with said signals to represent dark tones and middle tones and highlights of the original, with the cavity centers in successive lines diagonally staggered; and superimposing an auxiliary engraved pattern between successive rows of cavities in regions corresponding to highlights of the original, while controlling the engraving of the auxiliary pattern at a value corresponding to the particular highlight tone then being scanned, but not greater than that which is suflicient to remove the grid line connectors extending between adjacent cavities in the engraved plate.

5. The method of making an engraved half-tone plate for printing purposes, comprising forming engraved diamond-shaped cavities throughout the surface of the plate material of individual size corresponding to the tonal gradations of original subject matter, in a pattern diagonally staggered with reference to an edge of said plate, limiting the maximum cavity size to a value such that no adjacent cavity Walls intersect one another, thereby to define a pattern of spaced apart relatively narrow grid lines in plate areas corresponding to light tones of the original, and cutting away the material of said grid lines between their intersect-ions, along paths generally parallel to one another and to one edge of said plate.

6. The method of claim 5, in which the material of said grid lines is cut away along paths ofvarying width.

7. The method of claim 5, in which the material of saidgrid lines is cut away at a frequency double that of the primary frequency of dots, at a phase of 90 degrees relative to the primary row of dots, and at a depth proportional to they highlight signal.

References Cited in the file of this patent UNITED STATES PATENTS 577,373 Amstutz Feb. 16', 1897 1,273,993 Blecher July 30, 1918 2,005,130 Dalton June 18, 1935' 2,047,851 Bennett July 14, 1936 2,079,970 Speed May 11, 1937 2,258,124 Nichols Oct. 7, 1941 2,653,871 Marsh Sept. 29, 1953 2,699,720 Howey Jan. 18, 1955 2,718,548 Ielinek Sept. 20, 1955 2,738,730 Boyajean Mar. 20, 1956 2,768,577 Boyajean Oct. 30, 1956 2,863,000 Hell Dec. 2, 1958 2,899,493 Levine Aug. 11, 1959 

5. THE METHOD OF MAKING AN ENGRAVED HALF-TONE PLATE FOR PRINTING PURPOSES, COMPRISING FORMING ENGRAVED DIAMOND-SHAPED CAVITIES THROUGHOUT THE SURFACE OF THE PLATE MATERIAL OF INDIVIDUAL SIZE CORRESPONDING TO THE TONAL GRADATIONS OF ORIGINAL SUBJECT MATTER, IN A PATTERN DIAGONALLY STAGGERED WITH REFERENCE TO AN EDGE OF SAID PLATE, LIMITING THE MAXIMUM CAVITY SIZE TO A VALUE SUCH THAT NO ADJACENT CAVITY WALLS INTERSECT ONE ANOTHER, THEREBY TO DEFINE A PATTERN OF SPACED APART RELATIVELY NARROW GRID LINES IN PLATE AREAS CORRESPONDING TO LIGHT TONES OF THE ORIGINAL, AND CUTTING AWAY THE MATERIAL OF SAID GRID LINES BETWEEN THEIR INTERSECTIONS, ALONG PATHS GENERALLY PARALLEL TO ONE ANOTHER AND TO ONE EDGE OF SAID PLATE. 